1. Field
At least some example embodiments of the inventive concepts described herein relate to a semiconductor memory, and more particularly, to a storage device including a nonvolatile semiconductor memory and a controller, an operating method of the storage device, and an access method of accessing the storage device.
2. Related Art
A storage device refers to a device which stores data under control of a host device such as a computer, a smartphone, or a smart pad. The storage device includes a device, which stores data on a magnetic disk, such as a hard disk drive (HDD), or a device, which stores data on a semiconductor memory, in particular, a nonvolatile memory, such as a solid state drive (SSD) or a memory card.
The nonvolatile memory includes a read only memory (ROM), a programmable ROM (PROM), an electrically programmable ROM (EPROM), an electrically erasable and programmable ROM (EEPROM), a flash memory device, a phase-change RAM (PRAM), a magnetic RAM (MRAM), a resistive RAM (RRAM), and a ferroelectric RAM (FRAM).
To reduce manufacturing costs of the storage device, a technology is being developed for removing a high-capacity buffer memory like a dynamic random access memory (DRAM) from the storage device. In general, the buffer memory of the storage device is used to store metadata that is needed to manage a nonvolatile memory device of the storage device. For example, the metadata may include map data that includes mapping information between physical addresses of the nonvolatile memory device and logical addresses used by the host device.
If the high-capacity buffer memory like the DRAM is removed from the storage device, the metadata may be managed by using a small-capacity, high-speed buffer memory in a controller of the storage device. However, a capacity of the buffer memory of the controller is smaller than a capacity of the metadata, in detail, a capacity of map data. Accordingly, in the case where map data needed to perform a write request or read request from the host device is not loaded on the buffer memory of the controller, there is accompanied an operation of loading the needed map data from the nonvolatile memory on the buffer memory of the controller. This causes an increase in a time period that is needed for the storage device to respond to the write request or read request of the host device. In other words, operating speeds of the storage device and a computing device including the storage device are lowered.
Accordingly, devices and methods are needed to prevent a response speed or operating speed from being lowered even though the large-capacity buffer memory like the DRAM is removed from the storage device.